Thermodynamic Properties Of Glasses Research Articles

Low-frequency hybridized excess vibrations of two-dimensional glasses

One hallmark of glasses is the existence of excess vibrational modes at low frequencies ω beyond Debye’s prediction. Numerous studies suggest that understanding low-frequency excess vibrations could help gain insight into the anomalous mechanical and thermodynamic properties of glasses. However, there is still intensive debate as to the frequency dependence of the population of low-frequency excess vibrations. In particular, excess modes could hybridize with phonon-like modes and the density of hybridized excess modes has been reported to follow D exc(ω) ∼ ω 2 in 2D glasses with an inverse power law potential. Yet, the universality of the quadratic scaling remains unknown, since recent work suggested that interaction potentials could influence the scaling of the vibrational spectrum. Here, we extend the universality of the quadratic scaling for hybridized excess modes in 2D to glasses with potentials ranging from the purely repulsive soft-core interaction to the hard-core one with both repulsion and attraction as well as to glasses with significant differences in density or interparticle repulsion. Moreover, we observe that the number of hybridized excess modes exhibits a decrease in glasses with higher density or steeper interparticle repulsion, which is accompanied by a suppression of the strength of the sound attenuation. Our results indicate that the density bears some resemblance to the repulsive steepness of the interaction in influencing low-frequency properties.

Synthesis, Structure, and Heat Capacity of Some Basic Hydroxohalide Glasses of Zirconium and Hafnium.

This work highlights the synthesis and properties of novel basic hydroxohalide glasses of zirconium and hafnium. The hydroxohalide glasses are M(OH)4-αXα·(n)H2O where M represents either zirconium or hafnium, and X represents either chloride or bromide. The chemical structure is investigated using X-ray diffraction, total scattering, and the pair distribution function method to identify the local structure and any short-range connectivity. The thermodynamic properties of the glasses are probed using low-temperature heat capacity, where a gap in the phonon density of states is discussed and related to boson peaks in the heat capacity of the glasses. These results represent the first published synthesis and thermodynamic properties of zirconium and hafnium basic hydroxohalide glasses. Synthesis methods, structural determination, and analysis of the heat capacity data allow for a comprehensive look at the makeup and unique properties of these novel glassy materials. Values of the standard thermodynamic functions Cp,m°, Δ0TSm°, Δ0THm°, and Φm° are also reported.

Thermodynamic properties of silicate glasses and melts: VII. System MgO-B2O3-SiO2

Processes of evaporation and thermodynamic properties of glasses and melts of the system MgO-B2O3-SiO2 in the range of 1550–1800 K were studied for the first time by high-temperature mass-spectrometry. The resulting activities and Gibbs energies of components and also corresponding excess values point to negative deviations from ideal behavior and to the absence of immiscibility fields in glasses and melts of the system under study in the studied temperatures and concentration intervals.

Zero-point entropy of glasses as physical reality

Abstract This paper presents an analysis of the physical nature of the author’s results obtained since 1995 in the field of thermodynamics of the vitreous state (classic approximation). Excess entropy and free energy at 0 K are considered as the measures of non-equilibrium extent of glass with respect to crystal. Experimental data for melts and glasses of various chemical natures are generalized. A general form of the relations between reversible changes in free energy, enthalpy and entropy and their frozen values at the formation of any glass is shown. The problem of functional dissimilarity of the heat capacity of glass and that of crystal has been solved within the framework of the principle of free energy minimization as a result of self-organization of the vibration spectrum according to the frozen structure. The complete stabilization of glass structure at Kauzmann’s temperature or below it is forbidden by topologic reasons and (or) by thermodynamics. The effects of pressure on the thermodynamic properties of glasses are shown. Possible particular applications of the analysis of self-organization in chaotic systems are exemplified by the modeling of the abilities of neural systems.

Calculations of the thermodynamic properties of glasses and melts in the Cs2O-B2O3-SiO2 system in the framework of the generalized lattice theory of associated solutions

The possibility of calculating the thermodynamic properties of glasses and melts in the Cs2O-B2O3-SiO2 system formed by two glass-former oxides and one modifier oxide with the use of the vacancy variant of the generalized lattice theory of associated solutions is demonstrated. A comparison with the experimental thermodynamic functions determined earlier by high-temperature differential mass spectrometry and electromotive force method shows that the calculations performed within this approach lead to reliable thermodynamic functions. The thermodynamic properties and structural features (the relative numbers of bonds with due regard for the second coordination sphere) of glasses and melts in the Cs2O-B2O3-SiO2 system are analyzed in terms of the generalized lattice theory of associated solutions.

An Interstitialcy Theory of Structural Relaxation and Related Viscous Flow of Glasses

A theory of isothermal structural relaxation and creep of glasses below the glass transition temperature is given. According to the interstitialcy theory, the supercooled liquid state does not exist below a Kauzmann "pseudocritical" temperature T(k), which lies above the temperature T(K), commonly called the "Kauzmann temperature." Structural relaxation is simply a reduction with time of the interstitialcy concentration to the crystalline state for T<T(k), and to the metastable supercooled liquid state for T>T(k). The predicted viscosity eta is universal, given by eta=eta(0) + eta(T)t, in agreement with experiment. eta is continuous in T, with eta discontinuous at T(k) but linear in 1/T above and below T(k). The dependence of eta on the shear modulus directly connects kinetic and thermodynamic properties of glasses and liquids.

Structure, thermodynamic properties and cooling rate of glasses

The concepts of the thermodynamics of irreversible processes are used in order to derive expressions describing the dependence of the structure and thermodynamic properties of glasses on cooling rate. The temperature dependence of the thermodynamic potential of a frozen-in system is calculated and estimates are made for the deviation from equilibrium in vitrified melts. The theoretical results thus obtained are compared with experimental evidence on the thermodynamic properties of typical glass-forming substances and for vitreous metallic alloys. In this way basic kinetic and thermodynamic properties of the vitrification process are determined.